I think the theory is that the atmospheric noise is below the receiver's detection level so the noise you hear is generated inside the rig. Add a preamp and both the antenna noise and signal come up by the same amount bringing the antenna noise up to the detection floor and boosting the signal at the same time. The overall noise floor doesn't change much if any but switched from internal noise to antenna noise. The signal, however has come up and is easier to copy.
- Keith N1AS - - K3 711 - -----Original Message----- From: elecraft-boun...@mailman.qth.net [mailto:elecraft-boun...@mailman.qth.net] On Behalf Of DOUGLAS ZWIEBEL Sent: Monday, December 15, 2008 11:15 AM To: Elecraft Reflector Subject: [Elecraft] K3 sensitivity + preamp: looking for wisdom Hi... The following request for information is not specific to the K3 (or even to Elecraft). Please craft your response to be generic. Despite being an active ham/contester for over 40 continuous years (but not being an ee), I just do not understand how a "preamp" works. It is not a "smart" device, so how does it "know" to amplify the signal and not the noise? I first used a preamp way back when (1960's) when I was a teenager...it was an Ameco job. It was more "fun" than useful, because I could give out "big" S meter reports. Later, when listening in the noise became more important to my style of operation, I never could notice a difference between putting the preamp "on" and just turning up the volume (many rigs with built-in preamps too). Sometimes, turning up the AF gain worked better. So...HOW does a preamp help to "bring a signal out of the noise" without the use of some fancy computer algorithms backed by lots of computing power? Further, does a preamp really "improve" sensitivity? I have yet to find a signal that I could not copy (or hear) with any preamp "on" vs increasing the AF gain. PS...I am talking about HF. I know that lots of guys use a preamp on 160m with their beverages, so the effect must be real...right? HOW does a "dumb" device do it? de Doug KR2Q _______________________________________________ Elecraft mailing list Post to: Elecraft@mailman.qth.net You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com _______________________________________________ Elecraft mailing list Post to: Elecraft@mailman.qth.net You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com
